Various illumination techniques have been utilized in order to facilitate image capture, such as image capture in relatively low light conditions. For example, a flash that provides a pulse of visible light may be employed in order to illuminate a scene that is to be photographed. In instances in which the flash is integrated with the camera, the operational range of the flash, that is, the area or distance that is illuminated by the flash, may be restricted due to limitations in the illumination power and limitations in the capacity of the camera batteries that provide power for the flash. Additionally, a flash that draws power from the camera batteries may consume an undesirably large amount of power so as to limit the battery life.
A remote flash that is spaced apart from the camera and is powered by an external power supply may be utilized in order to at least partially overcome the limitations in illumination power and the challenges of power consumption. A remote flash may be triggered by the camera flash to illuminate a scene, thereby allowing for the illumination of a larger area or distance. Like a flash that is integrated with a camera, an external flash may have poor localization in that the flash illuminates everything in its vicinity. Also like a flash that is integrated with a camera, a remote flash generally operates in the visible spectrum of light and may therefore disturb or distort the visual scene for other observers. For example, in artistic or entertainment venues, such as a theater, a live music venue, or a video, television or film production, a visual scene may be the result of artistic vision that is utilized to bring the desired emotional message to the audience. However, a flash may disturb the visual scene and impair the artistic message that is intended to be conveyed by the scene.
In order to illuminate a scene without exposing the scene to levels of visible light that are distracting, techniques have been developed in which a scene is illuminated by a flash of infra-red (IR) light, either individually or in combination with visible light. By utilizing IR light, such as in combination with visible light, the colors of the resulting image remain true and correspond to the colors under ambient lighting conditions at the scene. One technique for obtaining an image of a scene that is illuminated with IR light and visible light is to capture a single image while the scene is concurrently exposed to both visible light and IR light. Alternatively, two images may be captured of the same scene with one image being captured while the scene is exposed to IR light and the other image being captured while the scene is exposed to visible light. In this technique, these two images of the same scene may then be combined. Various techniques may then be employed to combine the two images of the same scene captured while exposed in IR light and visible light.
Since illumination with IR light is invisible to the human eye, the IR illumination does not generally disturb or distort a scene or otherwise alter the message or mood to be conveyed by the scene. However, an IR flash that is integrated with a camera may have a limited operational range and poor localization and may also consume substantial power so as to limit the battery life of a hand held device, such as a camera, in a comparable fashion to a camera employing a visible light flash. As with a flash of visible light, an IR flash may be remote from the camera and, as such, may no longer draw power from the camera batteries and may have an improved operational range.
Although IR light is invisible to the human eye, illumination systems that combine illumination in both the visible and IR spectrums may still create images that deviate, to some degree, from realistic perception. In this regard, most lighting control systems presume the light is targeted towards the human visual system and operates in the spectrum that is visible to humans. As such, an image captured utilizing an illumination system that includes an IR component may appear different from the scene that the event's audience actually sees.
This situation may be considered undesirable, if realistic scene perception was supposed to be preserved in the digital image. Alternatively, this situation may be considered to be an artistic expression or a special effect addressed toward the digital image, if the lighting system can provide a controllable result to the digital image.